A number of technologies are applied in parallel to determine the molecular profile of a given biospecimen. The majority of these technologies currently use microarray based methods, but they are rapidly being supplemented and even supplanted by evolving next generation DNA sequencing technologies. Several varieties of microarray are used for various purposes, but the predominant current technical approaches use synthetic oligonucleotides bound to a solid support and interrogated with labeled nucleic acids prepared from the biospecimen of interest. The power of this approach in the current embodiment of this technology is based largely on the direct connection between known genome sequence and the design of microarrays completely controlled by computational means. This allows the investigator to construct arrays of arbitrary design tailored specifically to the desired analysis and to adjust the resolution of the arrays to a remarkably fine level. Thus, for example, it is now possible to determine the expression of mRNAs exon by exon and to observe changes in gene copy number (amplification or deletion) at better than single gene resolution. Fluorescent probes prepared from any cell or tissue source of interest are then hybridized to these arrays providing a large scale high resolution view of the genome. Currently we are focused on transitioning as many assays as possible to minute samples (such as may typically be collected in the course of routine clinical care) and formalin fixed paraffin embedded (FFPE) specimens. The ability to work with FFPE samples is particularly important when one considers the potential to transition discoveries made in the course of this work to clinical care where FFPE based methods are the standard method of stabilizing biospecimens in the clinical laboratory. Of importance we have demonstrated that it is possible to determine the methylation status of more than 400,000 CpGs in parallel on hundreds of samples with results which match those obtained from frozen specimens. This opens vast existing archives of FFPE samples to investigation. We now routinely obtain excellent copy number data from FFPE samples as well. We are particularly interested in the role of specific transcription factors in determining breast cancer phenotypes and have been investigating these through chromatin immunoprecipitation combined with microarray or sequencing analysis. We have recently investigated the epigenetic profiles of breast cancers using DNA methylation profiling. We demonstrated that there are two subsets of estrogren receptor alpha expressing tumors which can be sharply distinguished based on their methylation profiles. One of these which deviates from the methylation pattern of normal mammary epithelium has a markedly worse prognosis. We are interested in better characterizing this phenomenon and linking it to gene expression and its underlying biological mechanisms.